bytes, strings: allow Reader.Seek past 1<<31

Fixes #7654

LGTM=rsc
R=rsc, dan.kortschak
CC=golang-codereviews
https://golang.org/cl/81530043

src/pkg/bytes/reader.go

@@ -16,17 +16,17 @@ import (
 // Unlike a Buffer, a Reader is read-only and supports seeking.
 type Reader struct {
 	s        []byte
-	i        int // current reading index
+	i        int64 // current reading index
 	prevRune int   // index of previous rune; or < 0
 }
 
 // Len returns the number of bytes of the unread portion of the
 // slice.
 func (r *Reader) Len() int {
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		return 0
 	}
-	return len(r.s) - r.i
+	return int(int64(len(r.s)) - r.i)
 }
 
 func (r *Reader) Read(b []byte) (n int, err error) {
@@ -34,11 +34,11 @@ func (r *Reader) Read(b []byte) (n int, err error) {
 	if len(b) == 0 {
 		return 0, nil
 	}
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		return 0, io.EOF
 	}
 	n = copy(b, r.s[r.i:])
-	r.i += n
+	r.i += int64(n)
 	return
 }
 
@@ -49,7 +49,7 @@ func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
 	if off >= int64(len(r.s)) {
 		return 0, io.EOF
 	}
-	n = copy(b, r.s[int(off):])
+	n = copy(b, r.s[off:])
 	if n < len(b) {
 		err = io.EOF
 	}
@@ -58,7 +58,7 @@ func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
 
 func (r *Reader) ReadByte() (b byte, err error) {
 	r.prevRune = -1
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		return 0, io.EOF
 	}
 	b = r.s[r.i]
@@ -76,17 +76,17 @@ func (r *Reader) UnreadByte() error {
 }
 
 func (r *Reader) ReadRune() (ch rune, size int, err error) {
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		r.prevRune = -1
 		return 0, 0, io.EOF
 	}
-	r.prevRune = r.i
+	r.prevRune = int(r.i)
 	if c := r.s[r.i]; c < utf8.RuneSelf {
 		r.i++
 		return rune(c), 1, nil
 	}
 	ch, size = utf8.DecodeRune(r.s[r.i:])
-	r.i += size
+	r.i += int64(size)
 	return
 }
 
@@ -94,7 +94,7 @@ func (r *Reader) UnreadRune() error {
 	if r.prevRune < 0 {
 		return errors.New("bytes.Reader: previous operation was not ReadRune")
 	}
-	r.i = r.prevRune
+	r.i = int64(r.prevRune)
 	r.prevRune = -1
 	return nil
 }
@@ -116,17 +116,14 @@ func (r *Reader) Seek(offset int64, whence int) (int64, error) {
 	if abs < 0 {
 		return 0, errors.New("bytes: negative position")
 	}
-	if abs >= 1<<31 {
-		return 0, errors.New("bytes: position out of range")
-	}
-	r.i = int(abs)
+	r.i = abs
 	return abs, nil
 }
 
 // WriteTo implements the io.WriterTo interface.
 func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
 	r.prevRune = -1
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		return 0, nil
 	}
 	b := r.s[r.i:]
@@ -134,7 +131,7 @@ func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
 	if m > len(b) {
 		panic("bytes.Reader.WriteTo: invalid Write count")
 	}
-	r.i += m
+	r.i += int64(m)
 	n = int64(m)
 	if m != len(b) && err == nil {
 		err = io.ErrShortWrite

src/pkg/bytes/reader_test.go

@@ -27,8 +27,8 @@ func TestReader(t *testing.T) {
 		{seek: os.SEEK_SET, off: 1, n: 1, want: "1"},
 		{seek: os.SEEK_CUR, off: 1, wantpos: 3, n: 2, want: "34"},
 		{seek: os.SEEK_SET, off: -1, seekerr: "bytes: negative position"},
-		{seek: os.SEEK_SET, off: 1<<31 - 1},
-		{seek: os.SEEK_CUR, off: 1, seekerr: "bytes: position out of range"},
+		{seek: os.SEEK_SET, off: 1 << 33, wantpos: 1 << 33},
+		{seek: os.SEEK_CUR, off: 1, wantpos: 1<<33 + 1},
 		{seek: os.SEEK_SET, n: 5, want: "01234"},
 		{seek: os.SEEK_CUR, n: 5, want: "56789"},
 		{seek: os.SEEK_END, off: -1, n: 1, wantpos: 9, want: "9"},
@@ -60,6 +60,16 @@ func TestReader(t *testing.T) {
 	}
 }
 
+func TestReadAfterBigSeek(t *testing.T) {
+	r := NewReader([]byte("0123456789"))
+	if _, err := r.Seek(1<<31+5, os.SEEK_SET); err != nil {
+		t.Fatal(err)
+	}
+	if n, err := r.Read(make([]byte, 10)); n != 0 || err != io.EOF {
+		t.Errorf("Read = %d, %v; want 0, EOF", n, err)
+	}
+}
+
 func TestReaderAt(t *testing.T) {
 	r := NewReader([]byte("0123456789"))
 	tests := []struct {

src/pkg/strings/reader.go

@@ -15,17 +15,17 @@ import (
 // from a string.
 type Reader struct {
 	s        string
-	i        int // current reading index
+	i        int64 // current reading index
 	prevRune int   // index of previous rune; or < 0
 }
 
 // Len returns the number of bytes of the unread portion of the
 // string.
 func (r *Reader) Len() int {
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		return 0
 	}
-	return len(r.s) - r.i
+	return int(int64(len(r.s)) - r.i)
 }
 
 func (r *Reader) Read(b []byte) (n int, err error) {
@@ -33,11 +33,11 @@ func (r *Reader) Read(b []byte) (n int, err error) {
 	if len(b) == 0 {
 		return 0, nil
 	}
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		return 0, io.EOF
 	}
 	n = copy(b, r.s[r.i:])
-	r.i += n
+	r.i += int64(n)
 	return
 }
 
@@ -48,7 +48,7 @@ func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
 	if off >= int64(len(r.s)) {
 		return 0, io.EOF
 	}
-	n = copy(b, r.s[int(off):])
+	n = copy(b, r.s[off:])
 	if n < len(b) {
 		err = io.EOF
 	}
@@ -57,7 +57,7 @@ func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
 
 func (r *Reader) ReadByte() (b byte, err error) {
 	r.prevRune = -1
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		return 0, io.EOF
 	}
 	b = r.s[r.i]
@@ -75,17 +75,17 @@ func (r *Reader) UnreadByte() error {
 }
 
 func (r *Reader) ReadRune() (ch rune, size int, err error) {
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		r.prevRune = -1
 		return 0, 0, io.EOF
 	}
-	r.prevRune = r.i
+	r.prevRune = int(r.i)
 	if c := r.s[r.i]; c < utf8.RuneSelf {
 		r.i++
 		return rune(c), 1, nil
 	}
 	ch, size = utf8.DecodeRuneInString(r.s[r.i:])
-	r.i += size
+	r.i += int64(size)
 	return
 }
 
@@ -93,7 +93,7 @@ func (r *Reader) UnreadRune() error {
 	if r.prevRune < 0 {
 		return errors.New("strings.Reader: previous operation was not ReadRune")
 	}
-	r.i = r.prevRune
+	r.i = int64(r.prevRune)
 	r.prevRune = -1
 	return nil
 }
@@ -115,17 +115,14 @@ func (r *Reader) Seek(offset int64, whence int) (int64, error) {
 	if abs < 0 {
 		return 0, errors.New("strings: negative position")
 	}
-	if abs >= 1<<31 {
-		return 0, errors.New("strings: position out of range")
-	}
-	r.i = int(abs)
+	r.i = abs
 	return abs, nil
 }
 
 // WriteTo implements the io.WriterTo interface.
 func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
 	r.prevRune = -1
-	if r.i >= len(r.s) {
+	if r.i >= int64(len(r.s)) {
 		return 0, nil
 	}
 	s := r.s[r.i:]
@@ -133,7 +130,7 @@ func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
 	if m > len(s) {
 		panic("strings.Reader.WriteTo: invalid WriteString count")
 	}
-	r.i += m
+	r.i += int64(m)
 	n = int64(m)
 	if m != len(s) && err == nil {
 		err = io.ErrShortWrite

src/pkg/strings/reader_test.go

@@ -27,8 +27,8 @@ func TestReader(t *testing.T) {
 		{seek: os.SEEK_SET, off: 1, n: 1, want: "1"},
 		{seek: os.SEEK_CUR, off: 1, wantpos: 3, n: 2, want: "34"},
 		{seek: os.SEEK_SET, off: -1, seekerr: "strings: negative position"},
-		{seek: os.SEEK_SET, off: 1<<31 - 1},
-		{seek: os.SEEK_CUR, off: 1, seekerr: "strings: position out of range"},
+		{seek: os.SEEK_SET, off: 1 << 33, wantpos: 1 << 33},
+		{seek: os.SEEK_CUR, off: 1, wantpos: 1<<33 + 1},
 		{seek: os.SEEK_SET, n: 5, want: "01234"},
 		{seek: os.SEEK_CUR, n: 5, want: "56789"},
 		{seek: os.SEEK_END, off: -1, n: 1, wantpos: 9, want: "9"},
@@ -60,6 +60,16 @@ func TestReader(t *testing.T) {
 	}
 }
 
+func TestReadAfterBigSeek(t *testing.T) {
+	r := strings.NewReader("0123456789")
+	if _, err := r.Seek(1<<31+5, os.SEEK_SET); err != nil {
+		t.Fatal(err)
+	}
+	if n, err := r.Read(make([]byte, 10)); n != 0 || err != io.EOF {
+		t.Errorf("Read = %d, %v; want 0, EOF", n, err)
+	}
+}
+
 func TestReaderAt(t *testing.T) {
 	r := strings.NewReader("0123456789")
 	tests := []struct {